Capstone - Short CCT Temp Rise

Question 1

Thermoplastic V-75 & V-90 have a normal temperature limit of what?

Answer 1

75*C

Question 2

XLPE X-90 has a normal temperature limit of what?

Answer 2

90*C

Question 3

XLPE X-HF-110 has a normal temperature limit of what?

Answer 3

110*C

Question 4

Which table of the AS/NZS 3008 is used to determine temperature limits

Answer 4

Table 53

Question 5

What table of the AS/NZS 3008 is used to determine normal temperature of a conductor?

Answer 5

Table 1

Question 6

Table 52 of the AS/NZS 3008 is used to determine what?

Answer 6

Constant K

Question 7

What is the formula used to determine the time at which conductor insulation deteriorates during short circuit conditions?

Answer 7

I2 x t = K2 S2

Question 8

In the formula I2 x t = K2 S2 describe the meaning of each value

Answer 8

I = short circuit current
t = time
K = constant K
S = cross sectional area of cable

Question 9

Describe Clause 2.5.7.2.3 in the AS/NZS 3000

Answer 9

___

Question 10

When considering two circuit breakers, if C2 is >=800A then discrimination will be determined by using what?

Answer 10

Manufacturer’s data

Question 11

For most circuits, what is the discrimination between ratings?

Answer 11

C1 = 1.5 x C2

Question 12

For overloads when using HRC fuses, what is the discrimination between ratings?

Answer 12

F1 = 1.6 x F2

Question 13

For short circuits when using HRC fuses, what is the discrimination between ratings?

Answer 13

F1 = 2 x F2

Question 14

How do you determine discrimination when using both a circuit breaker and fuse?

Answer 14

A fuse and circuit breaker combination where the fuse is upstream and the circuit breaker is downstream shall be selected such that the characteristics of the devices provide discrimination between the overload curve and the instantaneous setting or short delay setting of C2 and the time-current curve for F1.

Question 15

What is the meaning of HRC for a fuse?

Answer 15

High rupturing capacity

Question 16

HRC and Current Limiting are referring to the same thing, True or False?

Answer 16

True

Question 17

The rated voltage for a fuse may be AC, DC, but not both. True or False?

Answer 17

False, it may be both

Question 18

What is a fuse’s current rating?

Answer 18

The value the link will carry continuously without affecting its’ characteristics.

Question 19

The minimum fusing current is the minimum current required for the fuse to conduct, True or False?

Answer 19

False - it is the minimum required to interrupt the circuit.

Question 20

A curve showing pre-arcing before interruption of a fuse is called what?

Answer 20

Time-current characteristics

Question 21

I1t is proportional to energy in what?

Answer 21

Amp-seconds

Question 22

Maximum instantaneous value of current that a fuse will let through during operation is called what?

Answer 22

Cut off current

Question 23

What are the three main regions of a trip curve for a Type C circuit breaker?

Answer 23

1 - Thermal region
2 - Electro-magnetic region
3 - Moving contacts region

Question 24

What are the three main regions of a Type C circuit breaker?

Answer 24

1 - Thermal region
2 - Electro-magnetic region
3 - Moving contacts region

Question 25

Which region of the trip curve for a Type C Circuit breaker has the shortest time?

Answer 25

Moving contacts region

Question 26

What is the part of a Type C circuit breaker that detects current overload?

Answer 26

Bi-metal strip

Question 27

What does an electromagnetic region of the trip curve for a Type C circuit breaker detect?

Answer 27

Short circuit

Question 28

I 1 = ____ x I N and refers to what?

Answer 28

1.13 Thermal non-tripping

Question 29

I 2 = ____ x I N and refers to what?

Answer 29

1.45 Thermal tripping

Question 30

I 3 = ____ x I N and refers to what?

Answer 30

5 Magnetic non-tripping

Question 31

I 4 = ____ x I N and refers to what?

Answer 31

10 Magnetic tripping

Question 32

On a 10A Type C MCB, 20A will cause the breaker to trip in how long?

Answer 32

10 - 45 seconds

Question 33

MCBs are designed to carry the nominal rated current at what temperature?

Answer 33

30*C

Question 34

IN = _____

Answer 34

Nominal tripping current

Question 35

Grouping factor K(g) is applied to what?

Answer 35

De-rating MCB thermal current

Question 36

If you have an enclosure with 3 MCBs to each supply 22A loads, with a 40*C ambient temperature, would 25A be suitable?

Answer 36

No, required to use 32A due to temperature de-rating

Question 37

Talk to assessor about what method of calculating cable impedence is preferred of the 1 options given.

Answer 37

1 - Using resistance only 2 - Using resistance and reactance only for cables bigger than 120mm2 and resistances only for cables 120mm2 or less. (b5.2.2) 3 - Using resistance and reactance only for cables bigger than 35mm2 and resistances only for cables 35mm2 or less. (b4.3) 4 - Using resistance and reactance for all components (transformer, mains, submains).

Question 38

Prospective fault current on equipment is usually marked in what value?

Answer 38

kA

Question 39

What is fault loop impedance?

Answer 39

A low enough circuit impedance that will draw a high enough current to operate the protective device within the required time

Question 40

Final subcircuits with GPOs <63A must be interrupted during a fault within what time?

Answer 40

0.4 seconds

Question 41

Portable equipment that can be moved during use and hand held Class 1 equipment must be connected to a final subcircuit which disconnects during a fault in how long?

Answer 41

0.4 seconds

Question 42

Circuits supplying fixed or stationary equipment must trip during a fault in how long?

Answer 42

5 seconds

Question 43

Impedance that is upstream of a protective device is considered to be what?

Answer 43

External

Question 44

Impedance that is downstream of a protective device is considered to be what?

Answer 44

Internal

Question 45

The fault path of an earth fault after the MEN link will be via what conductor? Why?

Answer 45

Neutral, PEN - because of larger cross-sectional area, meaning less resistance

Question 46

Table 8.1 provides what values? What does it take into account?

Answer 46

Maximum impedance values for the size and type of circuit breaker. ZEXT + ZINT

Question 47

If a calculated or measured value in a circuit exceeds that given for the device in Table 8.1, the circuit is compliant - True or False?

Answer 47

False it is non-compliant